Beta Amyloid and Presynaptic Nicotinic Receptors

描述（由申请人提供）：阿尔茨海默病的一个突出特征是使用神经递质乙酰胆碱的脑神经细胞的丧失。胆碱能神经元的丧失可能是毒性沉积物形成的结果，称为神经斑块，其中含有淀粉样肽作为主要成分。然而，淀粉样蛋白沉积与认知障碍之间的相关性似乎很差。另一方面，乙酰胆碱的靶受体可能受到影响，表明可溶性β淀粉样蛋白的作用。事实上，β -淀粉样蛋白最近被证明与神经元细胞体上的尼古丁受体直接相互作用。在大脑中，尼古丁受体的很大一部分定位于突触前神经末梢。初步发现β -淀粉样蛋白先激活后阻断离体海马神经末梢突触前尼古丁受体诱导的功能反应，但不影响与尼古丁受体共定位的密切相关的5-HT3 5-羟色胺受体介导的反应。因此，假设可溶性β -淀粉样蛋白通过破坏大脑突触后和突触前尼古丁受体选择性地改变神经元信号。本提案的具体目的是表征β -淀粉样肽对1)使用共聚焦显微镜在单个神经末梢中尼古丁诱导的钙反应和神经分泌的影响；2)微透析法观察体内神经递质释放；3)长时间β -淀粉样蛋白治疗引发神经末梢退行性反应，包括线粒体去极化和钙失调，以及蛋白质磷酸化在这些事件中的可能作用。在每种情况下，小鼠海马体、皮质以及纹状体（作为对照）都将被检查。使用近交系小鼠将允许使用转基因小鼠模型进行研究，包括APP突变体APPswe/PS1和尼古丁受体无突变体，从而可以明确确定哪些特定的突触前尼古丁受体亚基是β -淀粉样蛋白的靶标，以及慢性β -淀粉样蛋白对突触前尼古丁受体功能的影响。

DESCRIPTION (provided by applicant): A prominent characteristic of Alzheimer's disease is the loss of brain nerve cells that employ the neurotransmitter acetylcholine. Cholinergic neurons may be lost as a consequence of the formation of toxic deposits, known as neuritic plaques, which contain beta amyloid peptides as a major component. However, the correlation between amyloid deposition and cognitive impairment appears to be poor. On the other hand, target receptors for acetylcholine may be affected, indicating an action of soluble beta amyloid. Indeed, beta amyloid has recently been shown to interact directly with nicotinic receptors on neuronal cell bodies. In brain, a substantial portion of the nicotinic receptors are localized to presynaptic nerve endings. Preliminarily, it was found that beta amyloid first activates and then occludes presynaptic nicotinic receptor-induced functional responses in isolated hippocampal nerve endings, but does not affect responses mediated by the closely related 5-HT3 serotonin receptors co-localized with the nicotinic receptors on the same nerve endings. Thus, it is hypothesized that soluble beta amyloid selectively alters neuronal signaling via disruption of postsynaptic and presynaptic nicotinic receptors in the brain. The specific aims of this proposal are to characterize the effects of beta amyloid peptides on 1) nicotine-induced calcium responses and neurosecretion in individual nerve endings using confocal microscopy; 2) neurotransmitter release in vivo using microdialysis; and 3) initiation of nerve terminal degenerative responses to prolonged beta amyloid treatment, including mitochondria depolarization and calcium dysregulation, and the possible role of protein phosphorylation in these events. In each case, mouse hippocampus, cortex, and, on a limited basis as a control, striatum will be examined. The use of inbred mice will allow studies with transgenic mouse models, including the APP mutant APPswe/PS1 and nicotinic receptor null mutants, allowing definite determination of which particular presynaptic nicotinic receptor subunits are targets for beta amyloid and what effect chronic beta amyloid has on presynaptic nicotinic receptor function. Nicotinic receptors have been strongly implicated in memory mechanisms in the brain. Their disruption by elevated soluble beta amyloid may cause alterations in neuronal signaling in early Alzheimer's disease leading to reduced cognitive function. The role of presynaptic nicotinic receptors may be key, as these receptors are prominently localized to nerve endings in the brain. Characterizing the functional effects of beta amyloid on presynaptic nicotinic receptors may thus yield important information related to early events in Alzheimer's disease.